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2012: Best time to buy airline tickets

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2012: Best time to buy airline tickets01:10

The $0 fare and other wildly reduced fares appear to have been available for about 15 minutes, before United shut down its online reservations system, reporting that its site was undergoing maintenance.

"One of our filings today contained an error which resulted in certain fares being displayed as zero. We have corrected this error, " said United in a statement that also blamed human error for the mistake.